Thermal actuator

ABSTRACT

A thermal actuator provides an output force in response to a thermal input. The thermal actuator contains a thermally expansible and contractible material and may include a reservoir to store such material. The thermal actuator also may include condensation reducing, heat dissipating, and ambient temperature and pressure compensating components. Two thermal actuators may be coupled for selective bi-directional activation of a work element, such as a two position latch mechanism.

nited States Patent [1 1 111 3,805,528 ['45] Apr. 23, 1974 Huebscher THERMAL ACTUATOR [75] Inventor: Richard G. Huebscher, Clevelan Ohio [73] Assignee: Gould Inc., Chicago, Ill.

[22] Filed: Oct. 2, 1972 [21] Appl. No.: 293,790

[52] [1.8. CI. 60/530 [51] Int. Cl. F03g 7/06 [58] Field of Search 60/23; 165/105 [56] References Cited I UNITED STATES PATENTS 2,1 l5,502 4/1938 Vernet 60/23 UX 2,548,708 4/1951 Dickey 60/23 2,938,384 5/1960 Soreng et al.'. 60/23 UX 3,256,686 6/l966 Lindberg 60/23 X 3,525,670 8/1970 Brown 165/105 X' [5 7] ABSTRACT A thermal actuator provides an output force in response to a thermal input. The thermal actuator contains a thermally expansible and contractible material and may include a reservoir to store such material. The thermalactuator also may include condensation reducing, heat dissipating, and ambient temperature and pressure compensating components. Two thermal actuators may be coupled for selective bi-directional I activation of a work element, such as a two position latch mechanism.

25 Claims, 7 Drawing Figures I The invention relates to linear thermal actuators and systems to couple the same to do useful work, a thermal actuator being a device responsive to a thermal input to produce an output force.

Thermal actuators on this order generally comprise a casing with a movable piston forming a variable volume chamber in the casing. A thermally expansible and contractible material is sealed in the chamber, and when the material is heated to expansion, there is an increase in pressure on one side of the movable piston relative to the pressure on the other side'thereof causing it to move in the casing thus expanding the chamber. The movable piston is attached to an activator arm which may be coupled to do work as the piston is thus moved or driven.

Prior art thermal actuators have been plagued with numerous problems such as premature heating element burn-out, slow and inefficient operation since a large mass of material is heated and inefficient heat transfer techniques are' used, and limitation to operating in either vertical or horizontal attitudes. Also, prior art thermal actuators have experienced detrimental effects due to the influences of ambient temperature and pressure.

The instant invention encompasses a thermal actuator operable in all attitudes and which provides for more efficient heating of thermally expansible and contractible material. Such material may be solid, liquid, or gas which'expands, contracts, or partially or entirely changes phase with the application of thermal energy. Azeotropic liquid mixtures, either miscible or immiscible, for example, may also be used. The invention also includes a thermal actuator which so dissipates heat energy as to increase the speed of recycling when this is a factor, as is often the case. The invention further provides a thermal actuator which is compensated for changes in ambient temperatures and pressures that would otherwise alter its operating characteristics.

In'one form of the invention a liquid of the type that changes to gas phase'upon applicationof heat substantially fills the variablefvolume chamber of the thermal actuator, and efficient-electric heating permits heating only a minimumamount of the liquid to the boiling temperature, with a reservoir of the liquid provided not only' to improve the reliability and efficiency but also to prevent heater burn-out due to lack 'of liquid. This thermal actuator can be coupled to a special compensator for ambient temperature and pressure and further include a heat dissipator to decrease recycle time.

It is accordingly a primary object of the invention to provide a thermal actuator improved in the noted respects.

It is a further object of the invention to provide a thermal actuator which automatically compensates for potentially detrimental changes in ambient pressure and temperature.

It is another object of the invention to provide a liquid thermal actuator which boils only that part of the liquid substantially proximate to the heat source.

It is a still further object of the invention to provide such a thermal actuator having a reservoir of liquid to supply that part proximate the heat source.

It is still another object of the invention to provide a liquid vapor phase change type of thermal actuator which reduces undesirable condensation of in the actuator.

It is yet a'further object of the invention to provide a thermal actuator which dissipates heat to decrease the vapor recycle time.

It is yet another object of the invention to provide a thermal actuator which operates over a wide range of ambient pressures and temperatures.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described, the following description and the annexed drawing setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but several of the various ways in which the principals of the invention may be employed.

In the annexed drawing:

FIG. 1 is a simplified cross-sectional view of a basic liquid type of a thermal actuator;

FIG. 2 is a cross-sectional view of such a thermal actuator incorporating certain improvements of the present invention, shown in unenergized state;

FIG. 3 is a like sectional view of the thermal actuator of FIG. 2 in the energized state;

FIG. 4 is a schematic view of a thermal actuator provided with a heat dissipator in accordance with the present invention;

FIG. 5 is a simplified cross-sectional view of a combined thermal actuator and compensator in accord with the present improvements in unenergized state;

FIG. 6 is a like sectional view of the thermal actuator and compensator of FIG. 5 in the energized state;

FIG. 7 is a schematic cross-sectional view of two thermal actuators with a common compensator coupled to an external device for doing work.

Referring now to the drawing wherein like numerals refer to like elements in the several figures, a basic linear liquid thermal actuator generally indicated at 10 is shown in FIG. 1. This actuator includes a main body formed by a cylindrical casing 1 1 having a base 12 and an open end 13. Wires l4 and 15 pass through seal portions 16 and l7 in the base 12 to connect an electric heater 18 including a wound filament 19 to a source of energy, such as a battery or other power source, not shown. The heater may alternatively comprise a means for applying radiation or other energy to the thermal actuator. The casing 11 is fixed, for example, in a bracket or other holding means indicated generally at 20, and is covered at open end 13 by a cap 21. A movable piston 22 is positioned to slide in the casing 11, for example, between a first inner location 23 and a second extended location 24. The movable piston 22 should be in fluid sealed relation with casing 1 1, to form a variable volume chamber 25 in the actuator. Activator rod 26 is fixed axially to the piston 22 and passes through an opening 27 in cap 21 to be connected to transmit force to an external device, not shown, for doing work.

Variable volume chamber 25 is filled with a thermally expansible and contractible material heated by the heater 18 when energized. As heat is thus applied to such material, the pressure within the variable volume chamber 25, relative to ambient pressure, increases urging movable piston 22 to slide in the casing from the first location 23 toward the second location 24. The thermally expansible and contractible material may be, for example, a liquid which increases in volume as it is heated. Another useful material could be an azeotropic liquid which comprises a mixture of at least two liquids having different boiling points. Another example of thermally expansible and contractible material is a liquid which changes to gas phase as its temperature is increased. The gas requires more volume than the liquid thereby increasing pressure within the variable volume chamber to force movable piston 22 from the first location 23 to the second location 24 in the casing 11. Another example of thermally expansible and contractible material is a metal hydride, which may ingas and outgas upon change of temperature to vary the pressure within the variable volume chamber 25 to urge the movable piston 22 to slide in the casing thereby expanding the variable chamber and reducing the pressure therein. Other types of thermally expansible and contractible materials, such as, for example, oils, waxes, or alcohol, also may be used.

Although the thermal actuator is described as being responsive to the input of positive thermal energy, the invention is not limited to such. The thermal actuator also may be designed to be responsive to the input of negative thermal energy or cooling. For example, if the variable volume chamber 25 were filled with a liquid, such as water, the application of cooling to the water can cause a solid phase change requiring increased volume and therefore urging movable piston 22 from the first withdrawn location to the second extended location. Of course, a similar response would occur by application of cooling to a vapor to change same to a liq uid or solid requiring less volume and producing a suction force on the piston.

The thermal actuator more completely shown in FIGS. 2 and 3 in accordance with the present improvements includes an electric heater 31 for applying the thermal energy to a thermally expansible and contractible liquid 32 and a storage reservoir indicated generally at 33 to provide a constant source of liquid to the heater to prevent heater burn-out in the event-of sustained power input thereto. In FIG. 2, such thermal actuator is shown in the unenergized state, while in FIG. 3 it is shown in the energized state. A main cylindrical casing 34 having a flange 35 is coupled to an extension or guide casing 36 having a flange 37 by a clamp 38, and an impermeable rolling diaphragm 39 having a fold therein is held between flanges 35 and 37 to form a variable volume sealed inner chamber 40 and an open outer chamber 41. A movable piston 42 having an activator rod 43 attached thereto is reciprocable within the main casing 34 and guide casing 36. Wires 44 and 45 pass through portion 46 in the base 47 of the main casing 34 in electrically insulative relation and connect to a heater 31 which may be, for example, a spirally wound wire or metal foil element in the forward part of chamber 40.

The liquid storage reservoir 33 is defined by an absorbent porous washer 48 and an absorbent porous disc 49. The porous washer 48 comprises a wettable, electrically non-conductive wicking material, such as abestos filter paper or silica vitreous fiber having a relatively rapid wicking rate such as, for example, 0.5 inches in 0.1 second and is positioned proximate to the heater 31. Disc 49 comprises a wettable, electrically non-conductive wicking material similar to that of the porous washer 48 but having a lower density and wicking rate or absorbence and is located between the porous washer 48 and the base 47 of the main casing 34. A thermally insulating liner 50 is applied to cover the walls of the sealed chamber 40, and the piston 42 may also be made of a thermally insulating material.

Energization of this improved thermal actuator occurs when energy is applied to the heater 31 from a suitable source, not shown. Vaporization of the liquid in contact with the heater 31 occurs at a rapid rate due to the high watt density that can be employed in wick fed heaters as compared to heaters only submerged in free liquid. In the preferred embodiment of the invention, only that liquid in direct contact with such heater is vaporized to eliminate the need to heat all the liquid in the sealed chamber 40. As vapor is evolved at the heater, pressure builds up behind the piston 42 forcing it to extend, as shown in the drawing to the right, within the main casing 34 and coupled guide casing 36.

The impermeable rolling diaphragm 39 provides a good seal for sealed chamber 40 behind the piston 42 and requires minimal pressure to urge it to roll along its fold to form the enlarged sealed chamber 40 as shown in FIG. 3. The invention is not limited, however, to such a rolling diaphragm, and other similar sealing devices may be substituted therefor, or the diaphragm may be eliminated if the piston 42 forms a reliable seal otherwise with main casing 34 and guide casing 36.

During energization of the actuator, the thermally insulating liner 50 insulates the sealed chamber 40 from ambient temperature conditions to prevent recondensation of vapor due to a relatively cool ambient temperature. Vapor bubbles 51 form within and behind the porous washer 48 and provide further thermal insulation between the heater 31 and the casing 34. This vapor may pass through a central opening 52 in the porous washer 48 to reach the piston side of the heater 31. The liquid from disc 49 communicates with porous washer 48 via spaces between vapor bubbles 51 forming a storage reservoir to maintain the washer near saturation by the capillary transfer of liquid from a body of low wicking rate to a body of higher wicking rate. The volume of liquid contained in disc 49 can be varied by changing the thickness and pore volume of the disc, and the constant supply of liquid to the heater 31 prevents heater burn-out when the heater is energized for long periods of time.

After de-energization of the thermal actuator, 'condensate collects in the sealed chamber 40 on thermally insulating liner 50 and on rolling diaphragm 39 and is forced back to the reservoir 33 for the next activation. The rolling diaphragm 39 and piston 42 may be urged, as shown in FIG. 2 to the left, to the un-energized state by the external device to which activator rod 43 is connected by ambient pressure, or by an incorporated resilient spring 53 in chamber 41 acting against the piston, as shown in dotted outline in FIG. 3.

Because a small amount of liquid can yield a large volume of vapor, it is only necessary to heat the liquid proximate the heater 31. Although in the preferred embodiment the sealed chamber is substantially filled with thermally expansible and contractible liquid, such as for example Freon-l2, the constant supply of liquid from the reservoir 33 to the heater 31 enables efficient operation without a substantially liquid filled chamber at all position attitudes.

The thermal actuator 60 shown in FIG. 4 comprises a main body or casing 61 having a base 62 and an extension or guide casing 63. The casings are held together by a suitable coupling 64, and the guide casing 63 is movably held in a holding means or bracket by rollers 65. An activator rod 66 extends from the guide casing 63 and is connected to the movable piston located within the actuator. Main casing 61 is here held by a resilient spring 67 partially recessed in an opening 68 in a thermally conducting surface of a heat sink 69 for aiding dissipation of heat energy from the thermal actuator.

The thermal actuator thus shown in FIG. 4 may operate, for example, as the actuators described above; however, due to the action of the heat sink 69, the time required for recycling is decreased. Such decrease in recycling time is effected by utilizing reaction force applied by activator rod 66 on the thermal actuator to force the base 62 of the main casing 61 against the spring 67 between the heat sink69 and the base. When such reaction force exceeds the force exerted by the spring 67, the base 62 and the heat sink 69 are urged into abutment, thereby augmenting cooling of the thermal actuator as well as limiting temperature rise thereof and therefore preventing heater burn-out. Rapid cooling results in the rapid return of the thermal actuator to the unenergized ready state.

The thermal actuator system shown in FIGS. 5 and 6 includes an actuator as described coupled to an ambient pressure and temperature compensator 71 by an axial connecting rod 72. Other particular types of thermal actuators may be substituted in this system as will become evident from the following.

The liquid type thermal actuator 70 shown is unenergized in FIG. 5 and energized inFIG. 6. The boiling point of a liquid employed is dependent on both the temperature thereof and the pressure exerted thereon, and to operate efficiently over a wide range of ambient temperatures and pressures, it is desirable to maintain the liquid in the actuator at a condition slightly below the boiling point in the unenergized state. Such condition can be achieved by controlling the pressure of the liquid in the actuator by an auxillary means such as the compensator 71.

The actuator 70 comprises the usual main casing 73 secured to a holding means 74, such as the bracket or roller and bracket described above. The base 75 of the main casing 73 includes an insulated portion 76 through which wires or contacts 77 and 78 pass to a heater 79. A movable piston 80 positioned in the main casing 73 forms the sealed chamber 81 having a thermally expansible and contractible material 82 therein, while piston 80 is coupled by the connecting rod 72 to a movable piston 83 in the compensator.

The compensator 71 likewise includes a casing 84,

and the movable piston 83 therein forms a sealed chamber 85 also containing thermally expansible and contractible material 86. In the preferred embodiment of the system, the same thermally expansible and contractible material is used in both the thermal actuator and the compensator. The casing 84 of the compensator 71 may be firmly held in position or movably supported in a bracket or holding means 74 as described above with reference to the main casing 73 of thermal actuator 70. However, the main casing 73 and the casing 84 should always be maintained a fixed distance apart, for example, by interconnecting means, not shown. Such distance may be varied, though, for proper adjustment and balancing of the thermal actuator and compensator.

in such preferred system embodiment of the thermal actuator and compensator 71, the pistons and 83 have the same surface area. The compensator 71, however, is only partially filled with the thermally expansible and contractible material 85 whereas the thermal actuator 70 in the unenergized state is normally fully filled with the material 82. The remainder of the volume of the compensator chamber 85 is filled with vapor 87 of the liquid thermally expansible and contractible material 86. A basic property of liquid-vapor mixtures or solid-vapor mixtures results in the pressure within the compensator 71 being dependent upon the temperature of the mixtures, and such temperatures in the unenergized state will be the same temperature as that of the ambient air and the thermal actuator 70 regardless of the volume contained in the compensator chamber 85. In the unenergized state of the thermal actuator 70 the internal pressure forces on the pistons 80 and 83 are thus equal and oppose each other through the connecting rod 72. The connecting rod 72 is rigidly fastened to an external activator rod 88 which may be coupled for transmitting force to a device, not shown, for doing work. The forces produced by changes in atmospheric pressure on the pistons 80 and 83 will also be equal and opposite and nullify each other, thereby making the actuator assembly unaffected by ambient pressure changes.

Energizing the. heater 79 of the thermal actuator 70 raises the temperature and pressure in the chamber 81 of the thermal actuator, thereby forcing an increase in the volume of the chamber by a particular amount, the volume of the compensator chamber 85 being reduced by the same amount'of vapor therein condensing to liquid. It is desirable-to maintain a relatively constant temperature and pressure within the compensator chamber 85, i.e., relative to that in the actuator, and this may be achieved by filling the same with a spongy packing of small diamter metal wire mesh or similar equivalent material to serve as a heat sink for storing or supplying thermal energy and an extended surface for inducing condensation or vaporization.

Operation of the system shown in FIGS. 5 and 6 at a relatively high temperature is similar to operation at relatively low temperatures. With both the thermal actuator 70 and compensator 71 at the same temperature, there is no net force on the connecting rod 72, since pressures in the chambers 81 and 85 are equal and opposite, and the effect of atmospheric pressure is nullified, as described above. Vaporized liquid in the thermal actuator 70 produces a similar increase in pressure and piston motion as at the lower ambient temperature with an increase in volume in the thermal actuator and an equal decrease in volume in the compensator 71.

The thermal actuator 70 and compensator 71 system preferably uses liquid thermally expansible and contractible material, although other materials may be used as described herein. This system has the advantage .of maintaining the thermal actuator substantially full of liquid with a minimum of compressible vapors at a temperature close to boiling during the unenergized state at all ambient temperatures. Such advantage provides the most rapid response of the thermal actuator 70 to an increment of thermal input and the most rapid application of force via the activator rod 88. The thermal actuator 70 is capable of using a variety of thermally expansible and contractible materials, including liquids as indicated, such as the aforementioned Freonl2 or other suitable liquids which meet the requirements that ambient temperatures will always be above freezing temperature and below the critical temperature for boiling of the liquid. A further advantage of such a thermal actuator 70 combined with a compensator 71 is that the loss of a small amount of the thermally expansible and contractible material, from either the thermal actuator or the compensator has a minimal effect on performance as compared to a single thermal actuator configuration without a compensator.

A thermal actuator system using two thermal actuators and means to couple them together for selective operation of an external device 90, such as a door latch, is shown in FIG. 7. A first thermal actuator 91 for producing an output force responsive to thermal input having a body or casing 92 fixed to a support 93 has a movable piston 94 with a connecting rod 95 attached thereto. A variable volume chamber 96 is formed in the casing 92 by the piston 94 and is filled with the thermally expansible and contractible material 97. A heater 98, which may be coupled to a power source, not shown, by contacts 99 and 100 passing through an insulated portion of the base 101 of the casing 92, is positioned in the chamber formed by the piston 94 in the casing. A second thermal actuator 103 for producing an output force responsive to thermal input having a body or casing 104 fixed to a support 103 has a movable piston 106 with a connecting rod 107 attached thereto. A variable volume chamber 108 is formed in the casing 104 by the piston 106 and is also filled with thermally expansible and contractible material 109. A heater 110 with contacts 111 and 112 passing through an insulated portion of the base 113 of the casing 104, similar to the heater 98 described above, is positioned in the chamber 108 formed by piston 106 in the casing.

A common compensator 114 having a body or casing 115 supported on rollers 116 to roll or to slide along a fixed surface 117 is connected to the first thermal actuator 91 by rod 95. A piston 118 in the compensator 114 forms with the casing 115 a variable volume chamber 119 having, for example, a liquid 120 and vapor 121 thermally expansible and contractible material therein. The compensator piston 118 is also connected to the Second thermal actuator 103 by a rod 107. In the preferred embodiment of this system, the same thermally expansible and contractible material is used in each of the chambers 96, 108, and 119. Such thermally expansible and contractible material may be a liquid, such as, for example Freon-l2 or other materials as described above. The compensator 114 compensates for variations in ambient temperature and pressure and maintains the chamber of the unenergized thermal actuator 91 or 103 substantially full of liquid as described above with reference to FIGS. and 6.

Activator rods 122 and 123 are rigidly coupled to the connecting rods 95 and 107, respectively, and the ends 122, 123' thereof are positioned proximate a work element, such as a manual actuator 124 of a latch 90. The latch 90 can be operated through the are 125 by manual actuation or by selective automatic actuation of one of the thermal actuators 91 and 103. The manual actuator 124 of the latch 90 is preferably laterally bi-stable, as that when it is actuated to a central position it will then move forcefully to either the left or the right stop position, as desired.

In operation, power may be fed to the heater 98 of the first thermal actuator 91 for vaporizing a certain amount of liquid thereby increasing pressure on the piston 94 causing it to move connecting rod 95, activator rod 122, and manual actuator 124 to the right unlock position. During this operation the heater in the second thermal actuator is not energized and the manual actuator 124 remains in the unlock position. Selective energization of the thermal actuators 91, 103 may be achieved, for example, by a double throw center off switch (not shown). The chamber 96 of the first thermal actuator 91 will thus be held in expanded condition while the chamber 108 of the second thermal actuator 103 will remain in compressed condition and substantially filled with liquid.

To operate the thermal actuator system shown in FIG. 7 to move the manual actuator 124 through are back to the lock position, power is fed to the heater 110 of the second thermal actuator 103. A certain amount of liquid in the second thermal actuator 103 will then be vaporized increasing the pressure on the piston 106 of the second thermal actuator causing it to move the connecting rod 107, activator rod 123, and manual actuator 124 to the left lock position. The compensator 114 again compensates for all changes in ambient temperature and pressure as described above.

As can now be seen, the invention comprises a thermal actuator operable over a wide range of ambient temperatures and pressures, including means for preventing heater burn-out, for decreasing recycle time, and for compensating for ambient temperature and pressure. The several improvements in thermal actuators described herein may be applied either singly or in combination together with other thermal actuators to realize an improved linear thermal actuation for coupling to various types of external devices to actuate the same thereof or otherwise perform work.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A thermally actuated device, comprising main body means, movable piston means in said main body means, a variable volume chamber formed in said main body means behind the piston means, thermally expansible and contractible material in said chamber, means for storing a discrete quantity of-said thermally expansible and contractible material, said storing means comprising absorbent means, and means for applying thermal energy directly to a portion only of the said stored material to energize the device and thereby actuate the piston means.

2. A thermally actuated device as set forth in claim 1, further comprising means for at least partially insulating said thermally expansible and contractible material from ambient conditions.

3. A thermally actuated device as set forth in claim 2, wherein said means for insulating comprises thermal insulation means positioned within and encompassing said chamber.

4. A thermally actuated device as set forth in claim 1, wherein said material comprises a liquid for vaporization of said portion thereof when said thermally actuated device is energized, and said absorbent means contains that portion of the liquid to which the thermal energy is directly applied.

5. A thermally actuated device as set forth in claim 4, wherein said means for applying thermal energy comprises electric heater means positioned proximate to said absorbent means.

6. A thermally actuated device, comprising main body means, movable piston means in said main body means, a variable volume chamber formed in said main body means behind the piston means, thermally expansible and contractible material in said chamber, means for storing a discrete quantity of said thermally expansible and contractible material, and means for applying thermal energy directly to a portion only of the said stored material to energize the device and thereby actuate the piston means, said material comprising a liquid for vaporization of said portion thereof when said thermally actuated device is energized, said storing means comprising absorbent means containing that portion of the-liquid to which the thermal energy is directly applied, said means for applying thermal energy comprising electric heater means positioned proximate to said absorbent means, and the storing means comprising further absorbent means for absorbing the liquid and having a lower rate of absorbence than the absorbent means proximate to the heater means.

i 7. A thermally actuated device as set forth in claim 6, wherein the first mentioned absorbent means has an opening therein, with the same and the further absorbent means within said chamber and the latter substantially filled with the liquid.

8. A thermally actuated device as set forth in claim 1, further comprising means for biasing said piston means in said body means to maintain said chamber and said thermally expansible and contractible material substantially compressed when said thermally actuated device is not energized.

9. A thermally actuated device as set forth in claim 1, further comprising a distensible member in sealed engagement with said body means forming said chamber.

10. A-thermally actuated device as set forth in claim 9, wherein said distensible member comprises a diaphragm. for distension without stretching by rolling along a fold therein, thereby providing substantially no resistance to movement of the piston means.

1l. A thermally actuated device as set forth in claim 10, further comprising body extension means for extending movement of the piston means, and means for coupling said extension means to said body means and peripherally securing said diaphragm therebetween, energization of the device causing a portion of said liquid to vaporize increasing pressure in said chamber, said diaphragm and said movable piston means being urged into said extension means further to enlarge said chamber.

12. A thermally actuating device as set forth in claim 1, further comprisingmeans for extracting thermal energy from said device toeffect deactuation thereof.

13. A thermally actuated device, comprising main body means, movable piston means in said body means, a variable volume chamber formed in said body means behind said piston means, and thermally expansible and contractible material in said chamber, compensating means similarly formed and containing thermally expansible and contractible material, and means interconnecting the piston means of the main body and compensating means.

14. A thermally actuated device as set forth in claim 13, wherein said compensating means includes in the chamber thereof liquid and vapor in predetermined proportion.

15. A thermally actuated device as set forth in claim 14, wherein the thermally expansible and contractible material in the main body means comprises a liquid for vaporization when said thermal actuator means is energized, and said compensating means normally maintains said liquid substantially filling the chamber of the main body means when the device is not actuated.

16. A thermally actuated device as set forth in claim 13, wherein said thermally expansible and contractible material in said main body and compensating means comprises the same material.

17. A thermally actuated device system, comprising first means for producing a first linear output force responsive to thermal energy, second means for producing'a second linear output force responsive to thermal energy opposite to the first output force, means for mechanically coupling said first and second means, means for selectively operating the two, and means for connecting the coupling means to an external device for bi-directional actuation of the same.

18. A thermally actuated device system as set forth in claim 17, in which the external device comprises bistable actuator means having first and second stable positions, whereby operation of said first and second means moves the actuator between first and second stable positions of operation.

19. A thermally actuated device system as set forth in claim 17, wherein said first and second means each includes body means, movable piston means in said body-means, a chamber formed in said body means, thermally expansible and contractible material in said chamber, and means for applying thermal energy to said thermally expansible and contractible material to energize said respective first and second means.

20. A thermally actuated device as set forth in claim 19, wherein said thermally expansible and contractible material comprises a liquid for vaporization when one of said first and second means is energized and absorbent means is provided to retain the same within the respective chambers thereof. 7

21. A thermally actuated device as set forth in claim 20, wherein said means for applying thermal energy is electric heating means proximate said absorbent means.

22. A thermally actuated device as set forth in claim 17, wherein the coupling means includes means for compensating said first and second-means for changes in ambient conditions.

23. A thermally actuated device system as set forth in claim 22, wherein said compensating means comprises body means, movable piston means positioned in said body means, a chamber in said body means, and thermally expansible and contractible material in said chamber.

24. A thermally actuated device system as set forth in claim 23, further comprising means for movably supporting said body means of the compensating means for movement with the coupling means in both directions.

the heating means. 

1. A thermally actuated device, comprising main body means, movable piston means in said main body means, a variable volume chamber formed in said main body means behind the piston means, thermally expansible and contractible material in said chamber, means for storing a discrete quantity of said thermally expansible and contractible material, said storing means comprising absorbent means, and means for applying thermal energy directly to a portion only of the said stored material to energize the device and thereby actuate the piston means.
 2. A thermally actuated device as set forth in claim 1, further comprising means for at least partially insulating said thermally expansible and contractible material from ambient conditions.
 3. A thermally actuated device as set forth in claim 2, wherein said means for insulating comprises thermal insulation means positioned within and encompassing said chamber.
 4. A thermally actuated device as set forth in claim 1, wherein said material comprises a liquid for vaporization of said portion thereof when said thermally actuated device is energized, and said absorbent means contains that portion of the liquid to which the thermal energy is directly applied.
 5. A thermally actuated device as set forth in claim 4, wherein said means for applying thermal energy comprises electric heater means positioned proximate to said absorbent means.
 6. A thermally actuated device, comprising main body means, movable piston means in said main body means, a variable volume chamber formed in said main body means behind the piston means, thermally expansible and contractible material in said chamber, means for storing a discrete quantity of said thermally expansible and contractible material, and means for applying thermal energy directly to a portion only of the said stored material to energize the device and thereby actuate the piston means, said material comprising a liquid for vaporization of said portion thereof when said thermally actuated device is energized, said storing means comprising absorbent means containing that portion of the liquid to which the thermal energy is directly applied, said means for applying thermal energy comprising electric heater means positioned proximate to said absorbent means, and the storing means comprising further absorbent means for absorbing the liquid and having a lower rate of absorbence than the absorbent means proximate to the heater means.
 7. A thermally actuated device as set forth in claim 6, wherein the first mentioned absorbent means has an opening therein, with the same and the further absorbent means within said chamber and the latter substantially filled with the liquid.
 8. A thermally actuated device as set forth in claim 1, further comprising means for biasing said piston means in said body means to maintain said chamber and said thermally expansible and contractible material substantially compressed when said thermally actuated device is not energized.
 9. A thermally actuated device as set forth in claim 1, further comprising a distensible member in sealed engagement with said body means forming said chamber.
 10. A thermally actuated device as set forth in claim 9, wherein said distensible member comprises a diaphragm for distension without stretching by rolling along a fold therein, thereby providing substantially no resistance to movement of the piston means.
 11. A thermally actuated device as set forth in claim 10, further comprising body extension means for extending movement of the piston means, and means for coupling said extension means to said body means and peripherally securing said diaphragm therebetween, energization of the device causing a portion of said liquid to vaporize increasing pressure in said chamber, said diaphragm and said movable piston means being urged into said extension means further to enlarge said chamber.
 12. A thermally actuating device as set forth in claim 1, further comprising means for extracting thermal energy from said device to effect deactuation thereof.
 13. A thermally actuated device, comprising main body means, movable piston means in said body means, a variable volume chamber formed in said body means behind said piston means, and thermally expansible and contractible material in said chamber, compensating means similarly formed and containing thermally expansible and contractible material, and means interconnecting the piston means of the main body and compensating means.
 14. A thermally actuated device as set forth in claim 13, wherein said compensating means includes in the chamber thereof liquid and vapor in predetermined proportion.
 15. A thermally actuated device as set forth in claim 14, wherein the thermally expansiblE and contractible material in the main body means comprises a liquid for vaporization when said thermal actuator means is energized, and said compensating means normally maintains said liquid substantially filling the chamber of the main body means when the device is not actuated.
 16. A thermally actuated device as set forth in claim 13, wherein said thermally expansible and contractible material in said main body and compensating means comprises the same material.
 17. A thermally actuated device system, comprising first means for producing a first linear output force responsive to thermal energy, second means for producing a second linear output force responsive to thermal energy opposite to the first output force, means for mechanically coupling said first and second means, means for selectively operating the two, and means for connecting the coupling means to an external device for bi-directional actuation of the same.
 18. A thermally actuated device system as set forth in claim 17, in which the external device comprises bi-stable actuator means having first and second stable positions, whereby operation of said first and second means moves the actuator between first and second stable positions of operation.
 19. A thermally actuated device system as set forth in claim 17, wherein said first and second means each includes body means, movable piston means in said body means, a chamber formed in said body means, thermally expansible and contractible material in said chamber, and means for applying thermal energy to said thermally expansible and contractible material to energize said respective first and second means.
 20. A thermally actuated device as set forth in claim 19, wherein said thermally expansible and contractible material comprises a liquid for vaporization when one of said first and second means is energized and absorbent means is provided to retain the same within the respective chambers thereof.
 21. A thermally actuated device as set forth in claim 20, wherein said means for applying thermal energy is electric heating means proximate said absorbent means.
 22. A thermally actuated device as set forth in claim 17, wherein the coupling means includes means for compensating said first and second means for changes in ambient conditions.
 23. A thermally actuated device system as set forth in claim 22, wherein said compensating means comprises body means, movable piston means positioned in said body means, a chamber in said body means, and thermally expansible and contractible material in said chamber.
 24. A thermally actuated device system as set forth in claim 23, further comprising means for movably supporting said body means of the compensating means for movement with the coupling means in both directions.
 25. A thermally actuated device system as set forth in claim 21, further comprising further absorbent means for absorbently storing a quantity of said thermally expansible and contractible liquid in the respective chambers of said first and second means to supply liquid therefrom to the absorbent means proximate to the heating means. 